1. Field of the Invention
The present invention relates to a solid state device which responds to values of applied voltage by emitting radiant energy having a known frequency spectra with a predictable high frequency cutoff value .nu..sub.co for each value of applied voltage.
2. Description of the Prior Art
Numerous electroluminescent solid state devices have been developed, which emit relatively narrow bands of light in response to applied voltages. Such devices are commonly referred to as light emitting diodes (LED) and are commonly constructed as PN junctions wherein the injection of minority carriers into a conductivity type region provides the basis for carrier recombination and gives rise to a narrow band of radiation.
Visual observation of light emitted from metal-oxide-metal (M-O-M) sandwiches was described in early work by J. F. DeLord et al, in an article entitled "Correlation Between Electroluminescence and Electron Emission of Thin Metal-Oxide-Metal Sandwiches," which appeared in Applied Physics Letters, Volume 11, No. 9 Nov. 1, 1967, pages 287-289. In this article, thin sandwich structures of Be--BeO--Au and Al--Al.sub.2 O--.sub.3 --Ag, having oxide thicknesses of from 100 to 150 A, were described as being constructed to investigate the nature of electron emission. A first type of luminescence was reported as being a bright irreversible disruptive flash or sparking which permanently altered the characteristics of the device. A second type of luminescence was noted as a very faint bluish glow observed at a low current level on cooled devices. The DeLord et al article concludes that electron emission from the metal-oxide-metal sandwich structures was entirely due to the photoelectric effect caused by electroluminescence produced within the oxide layer.
Later work was described by H. Kanter in an article entitled "Comments on Correlation Between Electroluminescence and Electron Emission of Thin Metal-Oxide-Metal Sandwiches," which appeared in Applied Physics Letters, Volume 12, No. 8, Apr. 15, 1968, pages 243-244. That article indicated Al--Al.sub.2 O.sub.3 --Au structures, having oxide layers of 100 A, produce electron current dominated by photoelectron emission released in the top layer through electroluminescence radiation within the oxide at large field strenghts created by high voltages in excess of 8 volts.